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statx: reject unknown flags when using NULL path

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The statx() system call currently accepts unknown flags when called with
a NULL path to operate on a file descriptor.  Left unchanged, this could
make it hard to introduce new query flags in the future, since
applications may not be able to tell whether a given flag is supported.

Fix this by failing the system call with EINVAL if any flags other than
KSTAT_QUERY_FLAGS are specified in combination with a NULL path.

Arguably, we could still permit known lookup-related flags such as
AT_SYMLINK_NOFOLLOW.  However, that would be inconsistent with how
sys_utimensat() behaves when passed a NULL path, which seems to be the
closest precedent.  And given that the NULL path case is (I believe)
mainly intended to be used to implement a wrapper function like fstatx()
that doesn't have a path argument, I think rejecting lookup-related
flags too is probably the best choice.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Eric Biggers 2017-03-31 18:31:32 +01:00 committed by Al Viro
parent 75dd7e4bb6
commit 8c7493aa3e
1 changed files with 5 additions and 1 deletions
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6
fs/stat.c
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@ -130,9 +130,13 @@ EXPORT_SYMBOL(vfs_getattr);
int vfs_statx_fd(unsigned int fd, struct kstat *stat,
u32 request_mask, unsigned int query_flags)
{
struct fd f = fdget_raw(fd);
struct fd f;
int error = -EBADF;
if (query_flags & ~KSTAT_QUERY_FLAGS)
return -EINVAL;
f = fdget_raw(fd);
if (f.file) {
error = vfs_getattr(&f.file->f_path, stat,
request_mask, query_flags);